Effect of Fe additions on microstructure and mechanical properties of a multi-component Nb–16Si–22Ti–2Hf–2Al–2Cr alloy at room and high temperatures

•Microstructure of Nb–16Si–22Ti–2Hf–2Al–2Cr–xFe alloys is studied.•With Fe additions, Nb4FeSi silicide forms in addition to NbSS and Nb5Si3.•The solidification path dependent on the Fe content is primarily proposed.•At room temperature strength of the bulk alloy is improved by the Nb4FeSi.•At 1250 °C and 1350 °C, strength of alloy decreases with the Fe additions.

The phase constitutions, microstructural evolutions, and mechanical properties of Nb–16Si–22Ti–2Hf–2Al–2Cr–xFe alloys (where x = 1, 2, 4, 6 at.%, hereafter referred to as 1Fe, 2Fe, 4Fe and 6Fe alloys, respectively) prepared by arc-melting were investigated. It was observed that the nominal Fe content affected the solidification path of the multi-component alloy. The as-cast 1Fe alloy primarily consisted of a dendritic-like NbSS phase and (α+γ)-Nb5Si3 silicide, and the as-cast 2Fe and 4Fe alloys primarily consisted of an NbSS phase, (α+γ)-Nb5Si3 silicide and (Fe + Ti)-rich region. In addition to the NbSS phase, a multi-component Nb4FeSi silicide was present in the as-cast 6Fe alloy. When heat-treated at 1350 °C for 100 h, the 1Fe and 6Fe alloys almost exhibited the same microstructures as the corresponding as-cast samples; for the 2Fe and 4Fe alloys, the (Fe + Ti)-rich region decomposed, and Nb4FeSi silicide formed. The fracture toughness of the as-cast and heat-treated Nb–16Si–22Ti–2Hf–2Al–2Cr–xFe samples monolithically decreased with the nominal Fe contents. It is interesting that at room temperature, the strength of the heat-treated samples was improved by the Fe additions, whereas at 1250 °C and above, the strength decreased, suggesting the weakening role of the Nb4FeSi silicide on the high-temperature strength. As the nominal Fe content increased from 1 at.% to 6 at.%, for example, the 0.2% yield strength increased from 1675 MPa to 1820 MPa at room temperature; also, the strength decreased from 183 MPa to 78 MPa at 1350 °C.